This invention relates to broadband wireless communications between a base station and customer sites located within a geographical area and more particularly to an ATM Radio Interface Card (ARIC) for use in a cellular, broadband wireless communication system which combines multiplexing, switching and modulation schemes to provide both low and high bandwidth service functionality.
Broadband wireless systems such as Local Multipoint Distribution Systems (LMDS), known as Local Multipoint Communication System (LMCS) in Canada, are being developed to provide point to multipoint, high bandwidth services between a base station connected to a backbone such as an asynchronous transfer mode (ATM) network and network interface units (NIUs) at fixed locations within a defined geographic area or cell. A wireless link between the base station and the NIUs operates at a wireless radio frequency (RF) typically in the 2.5 to 40 GHz range depending on the allocated frequency license. A transmitter/receiver at the base station and a transceiver at each NIU site supports bi-directional, broadband xe2x80x9clast milexe2x80x9d communication between a service provider and a customer.
Traditional wireless access systems employ one polarization or another (vertical or horizontal, for example) as a means for delivering services over a radio medium to a given customer(s) site. These systems tend to be optimized for specific types of services that are largely dictated by the radio licensing structure and/or regulatory requirements.
With the advent of broadband licensing (LMDS/LMCS, for example), large numbers of different service types can be offered using a common delivery infrastructure. These varying services can be low bandwidth in nature (so called POTS, T1 or E1, fractional T1 or E1, Ethernet, or other, for example) or can be high bandwidth in nature (so called T3 or E3, OC-n, or other, for example).
Typically, the low bandwidth services are more cost effectively delivered through the sharing of radio resources. Sharing radio resources can be achieved by sharing resources in time, for example, using techniques such as time-division-multiple-access, (TDMA). This technique divides a given radio communication channel up into time slots which are allocated in a fixed or dynamic manner to the various customer-site equipment which are sharing this radio channel/resource. Although this tends to be more cost effective, this type of access technique commonly employs lower efficiency modulation schemes, quadrature-phase-shift-keying (QPSK), for example, which utilize more spectrum/license.
Typically the high bandwidth services are not as cost sensitive but demand much more capacity and therefore need to be connected using high efficiency modulation techniques, quadrature-amplitude-modulation (QAM), for example. These are not amenable to radio resource sharing and therefore are more optimally run within independent radio channels. The technique of using a number of independent radio channels serving one customer site each is referred to as frequency-division-multiplexing (FDM).
International PCT application WO 97/29559 by Evans et al, published on Aug. 14, 1997, and assigned to Standford Telecommunications, Inc. relates to a broadband wireless ATM system and in particular, discloses a protocol for effecting point-to-multipoint communications between a base station and a plurality of users. The protocol utilizes time-division-multiplexing (TDM) in the direction of the base station to the users (the downstream direction) and time-division-multiple-access (TDMA) in the direction of the user to the base station (the upstream direction).
The downstream and upstream transmissions are carried on radio frequency (RF) waveforms by either QPSK modulation or QAM modulation but not both concurrently.
This invention is applicable to wireless multipoint access systems that employ a cellular approach to provide service coverage to fixed customer sites within a given geographical area.
This is achieved by using shared radio access techniques which optimally allow multipoint connections of low bandwidth services as well as high bandwidth services to significantly enhance the use/applicability of broadband multipoint access systems.
Generally, the system includes interface means associated with a base station to accommodate both low and high bandwidth services and switching means at the base station to deliver the appropriate service.
Therefore, in accordance with a first aspect of the present invention there is provided an ATM radio interface card (ARIC) for use in a base station of a broadband wireless system for digital communication between an ATM backbone and a network interface unit (NIU) at a customer site over a wireless link, the ARIC comprising: a modem for modulating the digital communication from the ATM backbone; a tuner for converting the modulated communication to a radio frequency (RF) signal; and a control module for controlling transmission of the RF signal.
In a preferred embodiment of the invention the backbone is an asynchronous transfer mode (ATM) network and the radio interface means includes a pair, or more, of ATM radio interface cards (ARICs), one of a pair for TDMA and the second of a pair for frequency division multiple access (FDMA).
In accordance with a second aspect of the invention there is provided a method for communicating digital information between a base station and a network interface unit (NIU) over a wireless link comprising: providing at the base station an ATM radio interface card (ARIC) having a modem, a tuner, and a controller; configuring the digital information at the modem into an intermediate frequency (IF) signal; converting the IF signal into a radio frequency (RF) signal at the tuner; and delivering the RF signal to a transmitter for transmission to the NIU over the wireless link.